1. Field of the Invention
The present invention relates to methods for testing water for contaminants. In particular, the present invention relates to utilizing a contaminant concentration process for on-line contaminant testing of a continuous ultra pure water stream.
2. State of the Art
Ultra pure water (hereinafter xe2x80x9cUPWxe2x80x9d) is, simply, water with extremely low concentrations of contaminating materials. Such low contaminant concentrations make UPW a very efficient solvent. Thus, it is used in a wide range of industries including food processing and microelectronic device fabrication for cleaning products and process equipment without leaving behind contaminants that can adversely affect product quality. UPW is also used in biological processes, medical facilities, and pharmaceutical manufacturing which impose special purity requirements. UPW can be produced by a variety of techniques known in the art, but is primarily produced using dead-end filtration with polymeric membranes.
In the microelectronics industry, the use of UPW is critical, because active ions and solid particles in process water can result in the alteration of the current carrying characteristics of microelectronic devices by causing insulation breakdown and electrical shorts. In semiconductor devices, even minute particles less than a micron in size are able to destroy an entire wafer of semiconductor chips. Furthermore, even if a microelectronic device is not immediately destroyed by impurities, the impurities may affect the long-term reliability of the device.
With such a dramatic impact on device production, the microelectronics industry is continuously working toward making UPW even cleaner. However, water-purifying techniques for producing UPW have been improving more rapidly than the technology of on-line contaminant analyzers. In other words, UPW has become so clean that the ability to accurately test for contaminants on-line has become almost impossible. For example, current levels of individual contaminants, such as silica, metals, most anions and cations, and sodium, are in the parts per billion, even as low as parts per trillion. These levels are far below the existing lower detection limits of even the highest quality on-line analyzers.
Furthermore, an analyzer does not output the true contaminant level, because they also output a xe2x80x9czeroxe2x80x9d level created by the inherent signal noise of the analyzer. Thus, the contaminants concentration can become so low that the xe2x80x9czeroxe2x80x9d level begins to give false readings. Such erroneous data is very detrimental because knowing the true level of specific contaminants is crucial for the application of statistical process control monitoring techniques and true process alarming. Thus, water quality cannot be effectively monitored to prevent compromises in UPW quality before critical levels are reached.
Although laboratory analysis does have the capability to measure contaminants at the parts per billion and parts per trillion levels, the turn-around time from water sampling to assessment is far too long for real time monitoring.
Therefore, it would be advantageous to develop apparatus and techniques for on-line UPW testing to accurately measure and monitor minute levels of contaminants utilizing commercially available water purification equipment.
A contamination concentration device including a filtering device, which is feed a feed stream (containing a contaminant of interest) and which separates the feed stream into a product stream and a concentrate stream. The contamination concentration device further includes a contaminant analyzer which is feed the concentrate stream and which analyzes the concentration of the contaminant of interest in the concentrate stream. In general, the concentrate stream contains a higher concentration of the contaminant of interest than the feed stream.
The contamination concentration device is utilized by delivering the feed stream to the filtering device and separating the feed stream into the product stream and the concentrate stream. The concentrate stream is then delivered to the contaminant analyzer, which determines the concentration of the contaminant of interest within the concentrate stream. Using the determined concentration of the contaminant of interest, a concentration of the contaminant of interest within the feed stream is determined.